phthanite Min.
(ˈfθænaɪt)
[a. F. phthanite: named by Haüy 1822 (phtanite), f. Gr. ϕθάν-ειν to anticipate + -ite1, ‘because its thick schistoid texture and argillaceous character seem to announce beforehand its passage into schist’ (Traité de Mineral (ed. 2) IV. 546). Dana spells it -yte, as being the name not of a mineral but of a rock.]
A hard compact rock, consisting essentially of cryptocrystalline silica.
| 1868 Dana Min. 195 Cryptocrystalline Varieties [of Quartz]..13. Basanite, Lydian Stone or Touchstone, a velvety black siliceous stone..passes into a compact fissile, siliceous, or flinty rock, of grayish and other colors, called siliceous slate, and also Phthanyte. |